How is the mammalian eye adapted to its functions? KCSE Biology Essays

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Sclera/sclerotic layer; white fibrous layer; made up of thick connective tissue; protects the eye; maintains shape of eyeball;

Cornea; transparent; disc-shaped layer; that allows light to enter the eye; refracts light towards the retina;

Conjunctiva; delicate membrane; lining the inside of the eyelid; protects the cornea/eye;

Eyelids and eye lashes; thin muscle with hairs; protects the cornea/eye from mechanical/chemical damage/protects the eye from entry of foreign particles; protects retina from bright light;

Choroid; dark pigmented and membranous layer; that prevents light reflection within the eye/absorbs light; to prevent distortion of the image; has blood vessels; that nourish eye/retina/supply oxygen/remove carbon (IV) oxide and wastes; extends to form the ciliary body and iris;

Ciliary muscles; have elastic muscles that contract and relax; to alter shape/curvature of lens during accommodation;

Ciliary body; thickened front edge of the choroids layer; that produces aqueous humour;

Suspensory ligaments; made up of elastic connective tissue whose contraction and relaxation helps to adjust the shape of lens during accommodation/holds lens in position;

Lens; transparent; biconvex; balloon-like; it refracts light rays/focus light onto the retina;

Vitreous humour; nourishes cornea/lens; refraction of light; maintains eyeball shape;

Iris; thin circular ring; with circular and radial muscles; it gives eye colour/absorbs light; controls the amount of light entering the eye/adjusts size of pupil;

Pupil; an aperture through which light enters the eye;

Retina; has photoreceptor cells/rods/cones for image formation; generates impulses to the brain for interpretation;

Fovea/Yellow spot; with only cones; for high visual acuity/most sensitive part of the retina

Blind spot; point where nerve fibres emerge from the optic nerve/where optic nerve leaves eye/point where nerve fibres and blood vessels enter the eye;

Optic nerve; transmits impulses to the brain;

Muscles; inferior and superior oblique muscles; move eye from left to right; superior and inferior rectus muscles; move the eye up and down; external and internal rectus muscles steady the eye in its up and down movement;

Tear/Lachrymal glands; secrete a watery and saline fluid containing lysozymes/lytic enzymes/is antiseptic (tears); that moisten the conjunctiva and cornea; washes away dust and other foreign objects; kills microorganisms entering the eye;

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